1. Field of the Invention
The present invention relates to a method and an apparatus for channel impulse response estimation, and more particularly, to a method and an apparatus for channel impulse response estimation in global system for mobile communications (GSM).
2. Description of the Prior Art
As transmission rates increase, inter-symbol interference (ISI) due to multi-path propagation becomes one of the most serious problems in digital communication systems. The fading effect brought by multi-path propagation is a phenomenon of reflection and refraction of radio waves during propagation along different paths. The signals transmitted from the transmitter reach the receiver along different paths. These signals from different paths have various time delays and grades of attenuation. Hence the signals are affected by preceding and posterior signals, which is called inter-symbol interference. For the transmission distortion, the receiver of communication systems must estimate the characteristic of the channel and perform equalization relative to the channel in order to compensate the distorted signals and to obtain the correct signals. The compensation of channel distortion is evaluated by the accuracy of the channel estimation. For digital signals destroyed by additive white Gaussian noise (AWGN) and ISI, the maximum-likelihood sequence equalization (MLSE) is a well-known optimized equalization technique. For example, a method of channel estimation according to MLSE was introduced in U.S. Pat. No. 6,459,728 “Iterative Channel Estimation”. However, in most mobile communication systems, the channel impulse response (CIR), which is needed in the MLSE algorithm, is time-varying and unknown because of the relative move between the mobile station and the environment. Therefore, the estimation of parameters in CIR is the most important task for the equalization and channel estimation of receivers. Generally speaking, in receivers of the Global System for Mobile Communications (GSM), the CIR is estimated by utilizing known training sequence symbols.